Plant sterols, phytosterols, are cholesterol-like compounds that are found mostly in vegetable oils, nuts and legumes. There are about 44 sterols known to exist in plants. The most abundant phytosterols are, however, beta-sitosterol, campesterol, and stigmasterol. Phytosterols are not produced in the body. Thus, their sole source is diet.

Phytosterols have the same function as cholesterol in the body. Cholesterol is necessary component of cell membrane and required for the synthesis of sex hormones and bile acids. However, when cholesterol is high in the blood (serum) it is associated with heart disease. Plant-based diet rich in phytosterols is known to reduce serum total cholesterol and low density lipoprotein (LDL) cholesterol. On the other hand, diet based on animal food (meat, egg etc.) contributes to elevated serum cholesterol level.

For example, in one study it was found that subjects fed with wheat germ containing high phytosterol had 42% lower cholesterol in their blood as compared to those who were fed phytosterol-free wheat germ.

The mechanisms suggested on how phytosterols help reduce serum cholesterol include enhancing excretion of cholesterol, interfering with cholesterol synthesis, and competing for cholesterol acceptor sites in the intestinal walls.

Some animal studies have also shown that phytosterols inhibit or slow down tumor development.

On average, a conventional Western diet provides 250 mg/day of phytosterol. Whereas a vegetarian diet provides 2 times of that.

In the following table is a list of foods high/low in phytosterols. Generally, oils have high phytosterol content where as vegetables and fruits have lower content. The phytosterol content presented below is the sum of beta sitosterol, campesterol, and stigmasterol.